As is known, hydraulic adjusting or control cylinders are used for controlling the horizon or level of mining apparatus, with the aid of which cylinders the mining installation is tilted in the plane perpendicular to the stratification or its angular position in relation to the footwall horizon is adjusted, so that the mining machine which is guided on the face conveyor or on the machine guide is controlled either in the direction of a descent or in the direction of an ascent. For plough installations, the object is generally to control the level of cut of the plough so that the bottom pick of the plough always cuts on the footwall horizon, i.e. at the interface between the footwall rock and the coal seam, even if the seam stratification is irregular.
Amongst the various control systems which operate with hydraulic adjusting cylinders, those which have been proven in practice are primarily what are termed boom control systems or outrigger steering systems, in which the adjusting cylinders are integrated in boom rod assemblies attached articulated to the face conveyor on the stowing side, which boom rod assemblies are supported and guided in the advancing face support which generally consists of shield supports (see DE-OS 25 34 325, for example). In this respect the boom rod assemblies at the same time form the support advance mechanism, by means of which the face conveyor is moved in the direction of mining and the associated support frame is subsequently pulled behind.
In the control systems which have long been known for controlling the cutting horizon the adjusting cylinders are retracted or advanced by manual operation of their control valves if the plough runs out of the footwall horizon when the latter changes. This is often associated with oversteering of the plough installation, which can lead to deleterious loading of the conveyor and also of the support advance mechanism. Manual control of the adjusting cylinders does not enable faulty control operations reliably to be ruled out.
A method and a device are known for controlling the level of cut of a plough automatically (DE-PS 33 38 114). The cutting force loading of the cutter picks or the loading of the plough chain, and optionally the angular position of the face conveyor also, are determined in continuous operation, and the respective measured values are fed to an evaluation unit disposed on the plough control stand, which actuates the adjusting cylinders by way of a scheduled value/actual value comparison. A solution which can be used in practice for controlling the horizon of the plough installation is not given in the above document. Another disadvantage here is that the sensors are disposed on the plough body and are consequently subjected to considerable stresses when the plough is in operation. In addition, a separate power supply has to be disposed on the plough body, as does a transmitter which transmits the measuring signals via radio to the electronic evaluation and control unit.
With regard to plough installations, it is also known that the recognition sensors which detect the coal/footwall rock interface can be disposed on the chain-drawn plough body, the measuring signals of these sensors being utilised to adjust the bottom pick of the plough (DE-PS 35 09 868). With this arrangement also, a power supply and separate actuating drives with control elements for the plough tools have to be disposed on the plough body in addition to the recognition sensors.
For the recognition of the cutting horizon of mining machines such as coal ploughs or shearer loaders it has also been proposed in the prior art that optical sensor systems with sensor heads be used, which detect the different reflectances of footwall rock and coal and the measuring signals of which are utilised to control the tools of the mining machine (DE-PS 38 41 524). In addition to the optical sensor heads, a power unit for the supply of power, as well as transmitter and receiver stations for the sensor heads and control devices for adjusting the tools, has to be disposed on the mining machine or on the plough body in this case also.
Finally, a method and a device for controlling the horizon of a mining installation by computer-controlled adjustment of the stroke of the adjusting cylinders have been proposed in the prior art, in which, in order to move the height of the mining installation from an actual level to a scheduled level which is to be set, the stroke of the adjusting cylinders is automatically adjusted in steps by a control command which is sent to the level control electronics by the control computer according to the displacement of the mining installation over the displacement section towards the face, until the scheduled level is reached (German Patent Application P 42 34 720.3).